1. Field of the Invention
The present invention relates generally to projection lamps and, more particularly, to a compact projection lamp which is easily inserted into, and removed from, a socket.
2. Description of the Prior Art
Various electrical devices such as slide projectors, microfilm viewers, motion picture projectors, and so forth, employ an electric lamp as a light source to project a beam of light onto a film and thereafter to project an image onto a screen. These devices may be referred to generally as "projection systems" and the light sources used in projection systems may be referred to as "projection lamps." Projection systems also include a reflector disposed in proximity with the projection lamp to concentrate the light emitted by the lamp and focus the light into a beam. The beam of light is projected outwardly of the reflector along an axis, here termed the "optical axis." As long as the shape of the reflector remains constant, and so long as the lamp is not moved with respect to the reflector, the optical axis always is fixed with respect to the reflector.
Early projection systems employed relatively large electric lamps as the light source. Due to the size of the lamps, the reflectors also were quite large. Certain reflectors were made of glass having a silvered light-reflective coating. These glass reflectors were expensive to manufacture. Other reflectors were made of metal and, although not as expensive to manufacture as glass reflectors, these metal reflectors still were very large. The size of either glass or metal reflectors particularly was a serious limitation on the compactness of the overall projection system.
With the development of lamps operating on the so-called halogen regenerative cycle (see the Halogen Lamp Patent), advances have been made in reducing the size of the lamp and, hence, the reflector associated with the lamp. Advances also have been made in the composition and manufacture of the reflectors themselves. Because projection lamps are rigidly secured to the associated reflectors and because lamps and reflectors are employed in combination to project a beam of light, a combined lamp/reflector hereafter will be referred to where appropriate as a "lamp unit."
The First and Second Projection Lamp Patents describe commercially available lamp units. In these lamp units, the reflector is made in a cup-like, ellipsoidal shape and the lamp is secured within the concave portion of the reflector near the apex of the reflector. The reflector includes a base portion extending rearwardly from the apex of the reflector. The base portion includes an opening through which electrical leads extend to provide electric current to the lamp. In order to transmit electrical current to the lamp, pin connectors are secured to the leads. The pin connectors extend outwardly of the base portion and are adapted to engage electrical contacts carried in an appropriately configured socket. The lamp, electrical leads, and pin connectors are fixed with respect to the reflector by means of cement which fills the space between the base of the lamp and the reflector, as well as the opening in the base portion.
The foregoing arrangement of components does not address certain problems. Although the lamp units are much smaller than previous lamp units, they still extend an appreciable distance along the optical axis (from the front of the reflector to the rearwardmost end surface of the base portion). The pins extending outwardly of the base portion further increase this axial dimension. Projection systems are being made smaller than ever before, and the size of the lamp units presently available has compromised efforts to reduce the overall size of projection systems.
Another concern not addressed by prior lamp units is the connection between the cement and the reflector. This connection often is inadequate if the lamp and/or pin connectors are stressed. This concern arises, in part, because a typical present-day reflector employed with a lamp unit is made of a molded thermoplastic or thermoset material such as a phenolic. Presently available cements suitable for use in lamp units are sufficiently poor that an extremely strong bond cannot be maintained with the material from which the reflector is made. Accordingly, the pin connections often are loosened merely by inserting the lamp unit into the socket or by inadvertent mishandling of the lamp unit prior to insertion into the socket.
A further consideration with present day lamp units is that of replacing a defective lamp unit. Certain projection systems such as movie projectors require that the filament of the lamp lie in a predetermined plane, such as a horizontal plane or a vertical plane. Accordingly, the angular orientation of the lamp unit with respect to the projection system must be controlled. The positioning of the optical axis is critical, and thus the orientation of the reflector with respect to the projection system must be controlled. If a lamp should burn out during operation, it should be convenient to replace the lamp unit rapidly for minimum disturbance. Even though the heat developed by a lamp unit can be substantial, it is important that the lamp unit can be removed without requiring the operator to wait for it to cool. Moreover, when a new lamp unit is inserted into the projection system, the lamp unit should be capable of being inserted into the projection system with a minimum of difficulty and with quick, accurate orientation of the filament and the reflector.